Det-Tronics PW9200x Pathwatch IR Gas Detection System - Manual (Page 15)

ohms. The 4 to 20 ma output is surge protected.
The RATIO output in this manual is indicated in 0 to
10 vdc. For instruments using the 4 to 20 ma output,
the standard 0 to 10 vdc output can be read at the
RATIO test jack (brown) on the front panel or at the
receiver junction box when the OUTPUT SELECT
switch is set to the V position. In addition, a voltage
to current transfer curve is provided. See Figure A2.
CALIBRATION
The PathWatch system involves “line” rather than
“point” detection, monitoring the path between the
transmitter and the receiver. The instrument’s mea-
surement is a function of the gas concentration
(expressed in ppm) times the length of the path or
cloud (expressed in meters). Thus, the instrument’s
calibration is in units of PPM-Meters (PPM-M).
Because it is an open path system, the instrument’s
output reflects the average concentration over the
entire path length.
Simulated gas clouds and controlled gas concentra-
tions are used to factory calibrate the PW9200. The
response of a typical instrument is plotted on calibra-
tion graphs, which are included in the APPENDIX. A
calibration tube and a specified concentration of gas
can be used to check the instrument’s calibration
against the graph. The calibration graph is used to
determine the average ppm concentration in the
operational path length.
CALIBRATION EQUIPMENT
The optional calibration equipment for the PW9200 is
illustrated in Figure 7.
(1) Calibration Adapter
(1) Calibration Tube with flowmeter and hoses
If calibration equipment is not purchased, contact the
factory for calibration equipment or service.
PROCEDURE
The calibration of the instrument should be routinely
checked at least every twelve months, when there has
been a change in the type of hydrocarbon being
monitored, or when the operating path is changed
significantly. The instrument should be installed,
aligned and operating for at least one hour before
checking the calibration. This procedure is best per-
formed by two people.
NOTE
In order to ensure accurate calibration, this pro-
cedure should be accomplished when the path is
known to be free of hydrocarbon vapors.
13 95-8400
TRANSMITTER
MOUNTING SCREWS (4)
FLOWMETER INLET HOSE (5 1/2 FT)
FLOWMETER OUTLET HOSE
CALIBRATION ADAPTER
VENT HOSE (5 1/2 FT)
INFRARED TRANSMITTING WINDOW
CALIBRATION TUBE
FLOWMETER
REGULATOR VALVE
CALIBRATION GAS CYLINDER
Figure 7—Calibration Equipment